The most effective way to prevent people from looking into something is to poison the well. Attach the thing to something else obviously false, bonus points if evokes a negative emotional response.

Example; if someone decides to research 911, and instead of seeking out published papers and original sources, they go on yt and start watching videos about it, they will in short order hear a number of false things; holograms, lasers, nuclear weapons, missles, etc. Stuff that the average person would instinctively know is false.

The goal is not to convince the person that any of those examples is true. It's to associate them with other information and to game confirmation bias.

http://s3.amazonaws.com/nasathermalimages/public/video/prete... (win users might need videolan.org)